Optimization of VIM Targeting in Essential Tremor Surgery (Opti-VIM)

Deep brain stimulation (DBS) for essential tremor is based on the intermedius ventralis nucleus of the thalamus (VIM) stimulation. This structure is however very difficult to target, as it remains invisible on imaging. The current procedure based on awake surgery with clinical and electrophysiological testings has several limitations that lead us to develop a probabilistic model to locate precisely the target. This study aims to show that asleep DBS surgery based on this new targeting method leads to at least the same clinical results than the classical procedure.

The intermedius ventralis nucleus of the thalamus (VIM), which represents the target for deep brain stimulation (DBS) in essential tremor, still remains invisible on 1,5 tesla MRI (the only magnetic field available for stereotactic surgery). The target coordinates currently used are based on stereotactic atlases or mean coordinates from retrospective series. They are so imprecise that intra-operative clinical testing and micro-electrode recordings are mandatory to locate the exact position of the VIM. This procedure is long lasting, requires that the patient is awake, and increases the risk of intracerebral haemorrhage and nosocomial infections. Furthermore, some patients are not improved despite a DBS lead implanted in the electrophysiologically and clinically defined target. To overcome these limitations, investigators developed a probabilistic model based on data extracted from imaging of patients with particularly good outcomes after DBS surgery. This machine-learning model allows calculating to coordinates of the VIM according to the position of radio-anatomical landmarks with a mean precision of 1,65mm. The aim of this study is to validate this new targeting method on a prospective cohort of patients. DBS surgery will be performed under general anaesthesia, without intra-operative clinical and electrophysiological testing, with a surgical robot and under CT-scan guidance (O-Arm ©). Neurostimulation device programming will be performed as usual. Patients' tremor and quality of life will be evaluated pre and post-operatively at 3 months, according to the Fahn-Tolosa-Marin (FTM) scale and with an accelerometry recording (for tremor) and with the mPDQ-39 scale for quality of life. Surgical complications and side effects related to neurostimulation will be gathered all along the follow-up.

Essential Tremor, Deep brain stimulation, Ventro-intermediate nucleus of the thalamus, Targeting, Asleep surgery

DBS surgery will be performed under general anaesthesia, without intra-operative clinical and electrophysiological testing, with a surgical robot and under CT-scan guidance (O-Arm ©). The VIM coordinates will be calculated with the probabilistic model that have been developed.

Accelerometry recordings at the pre-inclusion visit and at 3 months after surgery in ON and OFF-stimulation conditions with spectral analysis.

Accelerometry recordings at the pre-inclusion visit and at 3 months after surgery in ON and OFF-stimulation conditions with calculation of the total accelerometry power.

rupture or displacement of electrode, pain at the stimulation box implantation site or along the subcutaneous cable if they require further intervention, infection.

Onset of dysarthria and ataxia assessed by the items 1 to 4 of the Scale for Assessment and Rating of Ataxia (SARA), ataxia assessed by a posturometry analysis, paresthesia, muscular contractions

Adaptation of Parkinson's Disease Questionnaire-39 to essential tremor Scale global range : min=0 / max=156 Higher values represent worse Quality of life

Coordinates of active contacts (i.e; the contact with the best effect on tremor without side effects) These coordinates (x, y, z) are obtained by merging the images of the 3-month postoperative scanner with the images of the preoperative MRI.

Inclusion Criteria: Severe essential tremor despite the optimal medical management Age between 18 and 75 years Normal MRI scan Mattis Dementia Rating Scale (MDRS) score ≥ 130 Affiliation to the social security Signed informed consent Exclusion Criteria: Depression (Beck Depression Inventory scale > 20) Contra-indication to surgery or general anesthesia Cerebral atrophy on MRI scan Pregnant or breastfeeding women